First Evidence for Mixing-Induced CP Violation in 𝐵0 𝑠 →𝐽/𝜓⁢𝜙⁡(1020) Decays in pp Collisions at √s = 13 TeV

Abstract

A novel machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27 500 tagged B s 0 → J / ψ ϕ ( 1020 ) decays from p p collisions at s = 13 TeV , collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb − 1 . A time- and flavor-dependent angular analysis of the μ + μ − K + K − final state, consistent with a ϕ ( 1020 ) → K + K − decay, is used to measure parameters of the B s 0 − B ¯ s 0 system. The weak phase is measured to be ϕ s = − 73 ± 22 ( stat ) ± 10 ( syst ) mrad , which, combined with the s = 8 TeV CMS result, gives ϕ s = − 75 ± 23 mrad . This value differs from zero by 3.2 standard deviations, providing the first evidence for mixing-induced C P violation in B s 0 → J / ψ ϕ ( 1020 ) decays. All measured physics parameters are found to agree with standard model predictions where available.